Method of injection molding and plastic part formed thereby

Abstract

A process for forming a plastic part having a tubular portion that is continuous and without any flash/mismatch due to mold parting lines in which an injection mold is provided having a cavity formed with a cylindrical surface portion and a core member removably inserted endwise into the cylindrical portion. A molten plastic material is injected into the cavity so that it extends into the cylindrical portion and around the core member. The core member is then withdrawn in an axial direction from the cylindrical portion after the plastic material therein has solidified enough to retain its tubular shape but before it has completely cooled to thereby enable the plastic material to shrink radially inwardly away from the cylindrical surface. Thereafter, the molded tubular shape and the cylindrical mold surface are moved relative to each other in an axial direction so that they are moved away from each other and the tubular portion is withdrawn from the mold, with the tubular portion yielding or flexing to whatever extent is necessary in order to clear the mold.

What is claimed is: 
     
       1. The method of forming a plastic part having a tubular portion with a radially enlarged lip at the terminal end thereof comprising: (a) providing an injection mold having a cavity formed with a cylindrical surface portion terminating in a groove located to form said lip, and a core member removably inserted in said cylindrical portion and configured to be in close proximity to said cylindrical surface adjacent said lip;   (b) injecting a molten plastic material into said cavity so that it extends into said cylindrical portion and around said core member,   (c) withdrawing said core member from said cylindrical portion along a line extending axially of said cylindrical portion after the plastic material in said cylindrical portion has solidified enough to retain its tubular shape but before it has completely cooled to thereby enable said plastic material to shrink radially inwardly away from said cylindrical surface; and   (d) thereafter providing for relative movement of said cylindrical surface portion and said tubular shape plastic material in a direction axially of said tubular shape to withdraw said tubular shape from said cylindrical portion, the close proximity of said core to said cylindrical surface adjacent said lip providing for a reduced wall thickness in said tubular shape adjacent said lip to enable deflection of said lip inwardly during said withdrawal.   
     
     
       2. A plastic part formed according to the process set forth in claim 1. 
     
     
       3. A plastic molded radiator part having a tubular portion for supporting a hose, said tubular portion being provided with a smooth external surface uninterrupted with any sharp protrusions that could extend into a hose on said tubular portion and having a radially enlarged external surface lip at the terminal end thereof and a reduced thickness wall portion at the terminal end. 
     
     
       4. A plastic molded radiator part according to claim 3 wherein said reduced thickness wall portion terminates on the inner surface of said tubular portion in a radially extending shoulder.